Earth boring tool



Feb. 20, 1945. I c, E. REED EARTH BORING TOOL Filed Jan. 2, 19

6 Sheets-Sheet 1 f%22 2209 zi id Feb. 20, 1945. I c, E EED 2,369,979

EARTH BORING TOOL Filed Jan. 2, 1940 6 Sheets-Sheet 2 Feb. 20, 1945. Q E R ED 2,369,979

RRRRRRRRRRRRR OL glwub/wtom f aii iz (2 152 6 0 FeB. 20, 1945. Q E REED 2,369,979

EARTH BORING TOOL Filed Jan. 2, 1940 6 Sheets-Sheet 4 {faraway fieeci Feb.20,1945 c, E. REE D 2,369,979

EARTH BORING TOOL Filed Jan. 2, 1940 s heets-$heet 5 [026226692 Md M entire area of the bottom of a bore hole.

Patented Feb. 20, 1945 i cago Pneumatic Tool Company, New York, N. Y., a corporation of New Jersey Application January '2, 1940, Serial No. 312,141

liiClairus- This invention relatesvto' earth boring tools of the type which includes a plurality of independently rotatable cutters for disintegrating the drills of this type, it isdesirable that the cutters be of the largest possible size so that the maximum number of teeth will be provided-upon them. Such large size cutters have an increased operating life and therefore the frequency with which the drills must be withdrawn from the bore hole for replacement of the cutters is reduced.

In accordance with the invention,- cutters of especially large size may be used in the drill. This is made possible by an improved cutter arrangement, and by the provision of supporting means for the cutters which dispenses with the necessity of a central hanger or other carrier for supporting the inner ends of the spindles for the cutters.

In the accompanying drawings vertical plane containing the axis of rotationoi 1 the side cutter 3.-

The side cutter I has a'base portion of generally cylindrical formation having teeth lalextending in an axial direction. and an inner portion of generally -frustoconical shape having teeth lb thereon- These teeth; are of the general 'formation disclosed in Reed Reissue Patent' No. 15,126, dated June 14, .1921. Due to the fact that the cutter l rotates in a plane which inclines upwardly towards'the' drill axis, the cutter teeth, of the base portion In cut an inclined area at the-side of the bore hole which includes clearance for thebit head 8. Within the teeth lb is formed a groove lc. The teeth lb cut an area upon the bottom of the bore hole which is in a generally horizontal plane, and

. this horizontal plane meets the inclined area cut Figure l is e, bottom plan view of one embodiment of the invention,

Fig. 2 is a section on the line 29-2 of Figure 1. only the cutters in the sectional plan being shown.

Fig. 3 is an elevation of' the spindle of Fig. 2.

Fig. 4 is a'section on the line H of Figure 1. Fig. 5 is a section on the line 5-5 of Figure 1. Fig. 6 is an end elevation of the bridge member shown in Fig. 3.-

Fig. 'l is a Plan view of Fig. 6. Fig. 8 is a section on line H of Big. 2.

Fig. 9 is a bottom plan view of another emhodiment of the invention. Fig. 10 is a section on the line il-Ifl of Big.

the righthand end of wardly to the junction point 1, and-is upon the by the teeth la at} point 1 indicated in Fig. 4.;

The cutter -2 rotates in a plane which converges upwardly towards the bit :head axis. Preferably this cutter is of the same diameter as the cutter Land. the teeth 2a. upon the base portion thereof operate upon the same inclined. area which is cut by the teeth la of the base portion oi cutter i. Theinner portion of the cutter teeth 20 are cut away to form agroove 2c. The area cut by the teeth 2b extends out-' teeth lb. 7

The side cutter 3 rotates in a plane which also converges upwardly towards the drillaxis. This cutter is of the same diameter as the other side cutters, and its teeth In track theinclined area at the side otthe bore hole which is entry the teeth to and 2a. The inner extremities of these 9, onlythe cutters in the sectional plan being iliustrated.

Fig. 11 is an elevation of the righthand end of the spindle oi Fig. 10.

Fig. 12 is an elevation of the bridge member V of Fig, 11 from the opposite side.

' Fig. 13 is asection on line l3 lI of Fig. 9.

Fig. 14 is a section on line "-44 of Pig. 9.

vention illustrated in Figs. l to 8, the side 'cutters L2, and 3 are rotatable about axes which ere disposed in radial planes of the bit which" are 120 from eachpther. The intermediate cutter 4 and thecentral cutter I are rotatable about ares which are disposed in the s'ame ili to the'iunction point- 1. The areas left" uncut by;

teeth are cut away by a groove Io. The teeth .31: upon the irus'to-conical portion of the cutter operate upon the horizontal area of the bottom ofthe bore hole, and cut outwardly;

- the groove 2c of cutter I and the'groove'lc of cutter 3 will be cutby the inner portionsoi the teeth In sothat inclined areaat the I side or the bore hole will be cut, The area left uncut by the groove is oi-cutteri will tegrated'bythe 2b and 'ab 01 the greater axial extent than the teeth it so as to Th a of mz'muauritne murmedmgeuem- 4 u e an mtolthe axiroirotction oithe Y bedisinothertwo side cutters. Preferably the teeth It will be of side cutter 3 so that the planes of rotation of these cutters converge upwardly within the bit head. This cutter preferably is of smaller diameter than cutter 3 and is offset below the side cutter 3, and its teeth operate upon the same horizontal plane which is cut by teeth lb, 2b, and 3b. The periphery of this cutter 4 is of generally frusto-conical formation. Preferably the outer extremity of the area cut by the teeth of cutter 4 extends to the inner extremity of the area cut by the teeth 2b. A groove 40 may be formed in the teeth.

The central cutter 5 is preferably of cylindrical formation and it rotates upon an axis which is horizontal so that its teeth act .upon the same horizontal plane upon which the teeth of cutter 4 and the teeth lb, 2b, and 3b act. By being disposed close to the axis a :c of rotation of the drill head, the teeth of cutter 5 disintegrate a circular area at the center of the bore hole, and this area extends outwardly to the inner extremity of the area cut by the teeth of cutter 4. Cutter 5 is disposed upon the opposite side of the bit head axis from the cutters 3 and 4.

The entire area of the bottom of the bore hole will consequently be cut by the five cutters. The area at the side of the bore hole which is of greatest extent will be disintegrated by the three tracking cutters I, 2, and 3, and the central part of the hole which is of lesser area will be disintegrated by the cutters 4 and 5. Because of the arrangement of these cutters so that their masses are substantially equally disposed about the bit head axis, a uniform cutting effect will result, and the drill will tend to cut a straight hole.

To support the cutter a side hanger 8 having a removable end spindle portion 9 is provided. The side hanger 8 is of the type disclosed and claimed in Patent No. 2,058,625 to C. E. Reed, dated October 27, 1936. The removable spindle portion 3 includes a stem I which is inserted in a bore hole I of the hanger 8, and these parts are held assembled by welding applied at I2. Within the spindle portion l3 of hanger 8 is formed a grooved raceway l4 to receive cylindrical anti-friction rollers |5.- The outer end of the spindle portion I3 is beveled at l6 and this surface l6 cooperates with a groove formed in the inner face of the flanged part of spindle portion 9 to constitute a raceway to receive frusto-conical anti-friction bearings l8. The interior of the cutter includes a cylindrical surface It! which bears upon the rollers I5, and an inchned surface 20 which bears upon the rollers It). At its innermost end the cutter includes a cylindrical surface 2| which has a frictional bearing contact upon the peripheral surface 22 of the flanged portion of the part 9.

To assemble the cutter and its bearings upon its hanger the bearings |5 are first disposed in place in the raceway l4. The cutter then is positioned axially over the spindle portion |3 to be disposed upon these bearings. The removable spindle portion 9 and the bearings iii are then assembled in place by inserting the stem ||l into the bore hole H of hanger 3. When assembled the rollers l8 prevent dislodgement of the cutter from its spindle. The frictional bearing surface at 2|, 22 tends to maintain the axial alignment of the cutter and the spindle.

The hanger 23 and the removable spindle portion 24 for supporting the side cutter 2 preferably are of the same formation of the hanger 3 iii) ascaovo and removable portion 3 for the cutter Thus the internal bearing surfaces of the cutter and the external bearing surfacesof the hanger 23 and removable spindle portion 24 provide raceways for the cylindrical roller bearings 25, the frusto-conical roller bearings 26, and the frictional bearing surfaces 2'1, which are of the exact dimensions of the corresponding portions for the cutter I. The fact that the teeth lb of cutter I cut an annular area at the bottom of the bore hole which extends further inwardly toward the drill axis than the area cut by the teeth 21), is due to the greater axial length of the cutter 1.

The cutter 3 is supported upon a hanger 30. which is similar to the hangers 8 and 23. The spindle portion 3| of this hanger, however, is of less axial extent, and the raceway for the antifriction roller bearings 32 also is of less axial extent. To retain the frusto-conical roller bearings 33 in place at the end of spindle 3|, a removable spindle portion 34 is provided which is retained in position by welding at 36 in a manner similar to that described for cutter The removable spindle portion 34, however, includes bearing surfaces for supporting the intermediate roller cutter 4 and the central roller cutter 5.

This support for the cutters 4 and 5 consists of a projection 31 extending from the opposite side of the enlarged flange portion 38 from the stem portion 35. Adjacent this flange 38 and in. the projecting portion 31 is formed a raceway 39 and a second raceway 40 for receiving the roller bearings 4| and 42, respectively, for the intermediate cutter 4. The raceways 39 and 40 converge inwardly toward each other, and the roller bearings ii and 42 preferably are of frusto-conical formation. In order to hold the roller bearings 42 against'displacement, a removable collar 43 may be afllxed upon av cylindrical surface 44 of the projecting portion 31, by means of a set screw 45.

To assemble the cutter 4 and its roller bearings in place, the roller bearings 4| are first located in the raceway 39, and then the cutter 4 is moved axially over the free end of the projecting portion 31 and upon the roller bearings 4|. The roller bearings 42 are then inserted within the cutter and upon the raceway 40 by movement through a notch 46 formed in the upper part of the surface 44. This notch 48 is closed by 2. lug 41 formed on the internal surface of the retaining ring 43. When the retaining ring 43 is in position, it therefore not only serves to prevent displacement of the roller bearings 42, but due to the arrangement and formation of these hearings, serves to retain the cutter 4 in place. I

To support the central cutter 5, raceways 48 and 49 are formed in the outer end of the projecting spindle portion 31 for frusto-conical antifriction roller bearings 58 and BI. The roller bearings 5| are held in place, and consequently the cutter 5 is prevented from axial displacement by a bridge or strut member 52 located upon the extreme reduced end portion of the projecting spindle part 31. In assembling the cutter 5, the roller bearings 50 are first located in the raceway 48. The cutter 5 is then passed over the free end of the spindle and upon the rollers 50, and the roller bearings 5| are then inserted into the cutter and upon their raceway 49. The bridge or strut member 52 which serves as a retainer for the cutter 5 may be afllxed to the projecting spindle portion 31 by means of welding applied at 53. l

aseaere bridge member 52 not only serves to retain cutter d in position, but it moreover serves as a support for the inner ends of the spindles for cutters i and 2. This constitutes an important feature of the invention because the inher ends of the removable spindle portions fi and 2d and the inner end of the spindle portion 31 receive support from each other, and the necescity for a central supporting element for these inner ends of the spindle is dispensed with. Because of the elimination of any central hangers or other supports, alLof the cutters, and particularly the side cutters, may be made of unusually large diameters.

In order that the bridge member 52 will have a firm bearing upon the inner ends of the spindle portions 9 and Ed, the outer extremities of the rule or this bridge member are faced oil at such an angle that flat surfaces 52a, 52b will be presented against the inner ends of the spindle portions Si and M. The necessary angular relation for these abutting faces of the extremities of the arms of bridge member is shown in Figs. 3, 6, and 7. Preferably the bridge member 52 will be welded to the faces of the spindle members i and 25 so that a solid formation will result. However, the invention contemplates the formation of the bridge member 52 and the spindie portions e and 2d in one piece, so that an extremely rigid construction will result. I

To position the cutter assemblies in the bit head, it is first necessary that the cutters i and '22 be assembled upon their hangers 8 and 23, respectively, together with their removable portions '3 and and that these assemblies be first aifilxed in proper position in the bit head. The assembly, including the side cutter intermediate cutter i, central cutter d, and its hanger and spindle portion 3d, together with the bridge or strut member 52, should be placed as a unit in the bit head so that the hanger 3b is in its proper position and the arms of the bridge member 52 will abut against the inner faces of the removable spindle portions 8 and 2d. The bridge member 52 may then be welded not only to the end of projecting spindle portion 371. but

the spindle portions 9 and 26 as well.

To direct flushing iiuid upon these several out.

here, a removable nozzle element 58 may be weld ed in place in. a central opening in the bottom oi the bit head. This nozzleelement should be formed with a plurality of openings so directed that each one of the cutters will receive a stream oi the flushing fluid. It is, of course, necessary that this nozzle element be located in place in the bit head before the cutters and their spindle sup-.

ports are afiixed to the bit head.

In the embodiment of the invention illustrated in Figs. 9 to 14, the same general arrangement of side cutters illustrated in the first embodiment oi" the invention is present. A principal difference of this second embodiment over the first embodiment resides in the fact that these, side cutters 55, 58, and 51 are of larger diameters so that the teeth upon their frusto-conical portions interfit. An additional distinction over the first eludes teeth 5511 which are divided at their central part by a deep groove 58c. At the inner end of the cutter, teeth 55b are formed upon a frusto- 4 conical portion of the cutter. Teeth 55a cut an inclined area at the side of the bore hole which includes clearance for the bit head, and teeth 55b cut an inclined area which slopes upwardly toward the center of the drill hole. These teeth 55a and 551) out the area at the junction of these two inclined areas.

Cutter 58 includes a base portion having teeth Ma which track the inclined area cut by the teeth 58a. Cutter 56 also includes teeth 56b upon a frusto-conical inner portion of the cutter, and which cut a separate zone upon the same inclined area determined by the teeth 55b. The teeth 56b are separated from the teeth 56a by a wide and deep groove 55c, and the teeth 56b bottom of the bore hole.

embodiment of the invention is that the central area of the bore hole is cut by a frusto-conical cutter 58 instead of by two cutters.

The side cutter 55 is rotatable about an axis which lies in the same radial plane of the bit head which contains the axis of rotation of the frusto-conical member 58, and this side cutter is of less axial length than the other two side cutters. The base portion'of side cutter II inare disposed so as to cut a path which is next inwardly from and does not overlap the path cut by the by the wide groove doc is cut by the teeth 55b and the adjoining portions of the teeth 55a of cutter t5.

Cutter '5! includes a base portion having teeth bid which track upon the same inclined area cut by teeth 55a and 56a.- and this cutter also includes teetht'lb upon a frusto-conical inner portion thereof which operate upon the inclined central area of the drill hole defined by the teeth 55b and 56b. Teeth 51?) cut a path upon this inclined central area which is next inwardly from the zone cut by teeth 55b. The wide groove 510 between teeth 51a and 5'"; therefore leaves an uncut area which-is disintegrated by the teeth 58b and by teeth 55b and the adjacent part of teeth 55a.

The frusto-conical cutter 58 is located adjacent the drill head axis and cuts a circular area at the center of the hole. The outer extremity of this circular area, extends nearly to the inner extremity of the annular area cut by the teeth 53b. The circular area which is cut by cutter 5t preferably is disposed in a' horizontal plane.

These four cutters, including the. three side cutters 55, 5S, and 51, and the central frustoconical cutter 58, thereby disintegrate the entire The outer portions of teeth 55a, 56a, and 51a out upon the same inclined area at the side of the drill hole. The

inner portions of teeth 58a and 51a track each other and cut the area left uncut by the groove of cutter 5b. The inner portions of teeth We cut the next inwardly disposed area from that cut by the teeth 56a and 51a, and this area cut by the inner portions of a extends up to thejunction point of the inclined side zone and the inclined next inwardly disposed zone. Teeth 55b, 56b, and 51b cut progressively inwardly dlsposed areas of the bottom of the drill hole from the junction point aforesaid up to the circular area cut by the frusto-conical cutter 58. As has been noted, the teeth 55b, 56b, and 51b all operate upon the same inclined or generally conical .surface disposed between thehorizontal area cut by cutter I8 and the inclined side area.

On reference to Fig. 9 it will be observed that the teeth at the inner portions of the cutters 55, I, and 5] interflt or intermesh with each other. Thus the teeth 55b and the inner. adjacent portions =01 teeth 55a enter into the groove 560 of c tt r". and the teeth 56b and teeth 55b therefore overlap. Teeth 58b extend into groove 510 of cutter '51 during the rotation of these cutters,

and the teeth 31b and "b therefore overlap each teeth 55?). The area which is left uncut other. Teeth 55b extend into groove 510 of cutter 51 during the rotation of these cutters, and the teeth 55b therefore overlap the teeth 511), although they are separated by a space which corresponds to the thickness of teeth 56?). Due to this interfitting relationship between the teeth of the several side cutters, they may be made of considerably larger diameter than the side outters of the first embodiment of the invention, and

this enlarged size of the cutters is made possible, as has been stated, because of the absence of any central supporting members dependingbecause the outermost portion of the hole is of greatest area. The center cutter disintegrates an area that is relatively small and its radius short. In thi invention, the center cutter is designed for strength enough not to break, and for a minimum of work for high bit efliciency, and the emphasis respecting the center cutter is on its relative over-all or axial length, or annular path width. The three side cutters are relatively large and have ample bearings. The relationship stated above effects high operating efliciency of tooth penetration, speed of bit operation, and bit durabiliiw, because the heavy operating loads fall upon the side cutters and not on the center cutter, and the center cutter, being relatively small and of short radius respecting its annular path, does not ride the earth formation it is intended to cut. Long center cutters do ride the formation. The side cutter tooth arrangement of this invention is not possible with a long center cutter. Riding" retards bit advance or penetration and reduces speed of operation, and increases destructive effects of the bit contacts with bottom.

Cutter 55 is carried upon a hanger 66 having a projecting spindle portion 6| which provides a grooved raceway 62 for receiving cylindrical antifriction bearings 63 and a grooved raceway '64 for receiving frusto-conical anti-friction rollers To retain the bearing 65 in position and thereby prevent displacement of the cutter 55, a removable sp ndle portion 66 is attached-to the hanger 60. This removable spindle portion 66 includes a flanged enlargement 61 which pro- Vides an inner face contacting the outer ends of rollers 65, and also provides upon itsperiphery a cylindrical frictional bearing surface 68. The cutter 55 includes internal surface which bear upon the rollers 63 and 65, and also includes a bearing surface which frictionally engages the outer periphery 68 of flange 61.

To assemble the cutter 55, the bearings 63 are first located in their raceway 62, and the cutter 55 is then placed in position upon the spindle. The frusto-conical bearings 65 are then placed in position upon their raceway 64, this being made possible by the large size of the internal surface of the cutter which'bears .upon the peripheral surface 68. The removable spindle member 61 is then located in position by inserting its stem portion 69 in the bore within the spindle portion 6|. l

The frusto-conical cutter 58 is rotatably mounted upon the projecting portion 1! of the removable spindle portion 66. This projecting portion 1| is on the opposite side of flanged enlargement 61 from the stem portion 69, and

the spindle portion H is offset below the axis of the stem portion 69. At the junction of the projecting spindle portion 1| and the flange 61, is formed a raceway 12 for receiving frusto-conical anti-friction rollers 13. Next along the length of the projecting spindle portion 1| are formed raceways 14 and 15 to receive cylindrical antifrictional roller bearings 16 and 11, respectively. In assembling this cutter, it is necessary that these several roller bearings be in position in their raceways so that the cutter may be inserted over the free end of the spindle to bring its internal bearing surfaces upon these roller bearings. To retain the cutter 58 in place, a bridge or strut member 18 is positioned upon the reduced free end portion 19 of spindle portion 1|, the inner end of the frusto-conical cutter bearing directly against the inner side face of this bridge or strut member.

Cutters 56 and 51 preferably are supported upon side carrier assemblies which include a hanger and a removable spindle portion similar to those for cutters I and 2. As shown in Fig. 13, the cutter 51 is carried upon a side hanger 8| and its complemental removable spindle portion 82. The cutter rotates upon cylindrical rollers 83, frusto-conical rollers 84, and frictional bearing surfaces at 85.

The support for cutter 56 which includes hanger 86 and its removable spindle portion 81 preferably is of the exact formation of the support for cutter 51 to simplify fabrication and replacement. Rollers 88 and 89 and frictional bearing surfaces at 90 rotatably mount the cutter 56. The internal bearing surfaces of cutter 56 necessarily are in the same relation to each other as the internal bearing surfaces of cutter 51 since they are mounted upon identically formed supports.

The dotted line, Fig. 9, represents'the wall of the bore hole generated by the drill, and it will be observed from Fig. 9 that the three side outters are symmetrical in arrangement and the diameters are uniform and largest that could be selected 'for the cutters that would rotate freely without excessive digging into the side wall of the hole, and that the annular paths of the respective rows of teeth are substantially the same width for each cutter, measured radially of the drill; but all of the rows do not track each other,

and the over-all width of the three cutters is more than the total width of effective cutting edges of the teeth.

The manner of assembling the cutters and their carriers in the embodiment of the invention illustrated in Figs. 9 to 14, inclusive, is similar to that for the first embodiment of the invention. As with the first, embodiment of the invention. it is necessary that the nozzle member 9| be first affixed at the lower end of the bit head. The

cutters 56 and 51 and their carriers are then affixed in the bit head, and thereafter the assembly, including the side cutter 55 and the central frusto-conical cutter 58 is affixed in the bit head so as to bring the faces 18a, 18b of the arms of the bridge member 18 against the inner faces of removable spindle portions 82 and 81 for cutters 56 and 51 respectively. Welding may then be applied to secure the bridge member 18 to the reduced spindle end ll and to the faces of the spindle members 82 and 81.

Fig. shows a construction in which the removable spindle sections are formed integrally with the central bridge member. In this figure, the central bridge member 83 has formed lutegrally with it and at one end thereof a flange 94 from the side face of which projects the stem 95. To the other end of the bridge member 83 is integrally formed a flange 86 from the side face of which projects a stem 91. Into the side of flange 94 from which the stem 95 projects is formed a groove 88 to constitute a raceway for anti-friction bearings. A similar groove 89 is formed in the side lace of flange 86 to receive other anti-friction roller bearings. Through the central part of the bridge member 93 may be formed a bore hole to receive the free end of a roller cutter supporting spindle. The integral formation shown in Fig. 15 may be employed instead of the separate bridge member 52 shown in Figs. 6 and '7 and the separate removable spindle sections 9 and 2 shown in Figs. 4 and 5. If desired, the bridge member I8 shown in Fig. 12 maybe integrally formed with the removable spindle portions 82 and 811 shown in Figs. 13 and id.

In the assembly of an earth boring tool employing the integral bridge and removable spindle section of Fig. 15,- the entire cutterassemblv side cutters. two of said cutters each having a would be made with the spindle supports apart from the bit head. That is, ii this integral member were to be employed in the construction of Fig. 1, the side cutter i and its anti-friction bearings and the side hanger 8 would be associated with the stem 91 and flange 88. In like manner, the cutter 2 and its anti-friction bearings and hanger 23 would be associated with the stem 95 and flange M. The assembly consisting'of the side cutter 8 and cutters l and I, together with the hanger Ill, would then be made. and the free end of the spindle 31 (shown in dotted lines) of this assembly would be inserted in the bore hole through the bridge member .3. The complete assembly thus made. would then be attached to the bit head by inserting the shanks oi the side hangers I, 23, and ll upwardly into their respective recesses in the bit head.

It is to be understood that it will be entirely possible to substitute for the side cutters shown in Figure 1 the side cutters shown in Fig. 9. or

conversely, to substitute for the side cutters of Fig. 9 the side cutters 01 Figure 1. Other similar modifications of the invention are within the scope of theinvention. For example, instead of a bore in the bridge member, a slot may be formed therein opening downwardly so that the spindle end beyond the central cutter may be dropped therein when the assembly ismade. The slot would then be closed by welding.

In both embodiments of the invention the presence of thebridge member joining the inner ends of the three spindl or'cutter sup orts, results in an extremely rigid formation since each spindle receives support from the other two. 137 mounting the bridge member upon one of the spindles and providing it with broad bearing faces to abut the inner ends of the other two spindles,

the forces imposed upon it are adequatel sustained. In both instances illllstl'lted, the hearing faces or the bridge member are generally opbase row of teeth positioned outermost of the drill and of substantially coextensive length whereby they track the same annular area at the side of the bore hole, said cutters also each hav-- ing another row of teeth spaced from the base row of teeth and positioned at diirerent distances therefrom whereby they cut separate but adjoining areas upon the hole bottom, the third cutter having a base row of teeth of less length than the base row of teeth on said two. cutters and positioned at the side of the drill whereby it tracks only the outer portion of the area tracked by said two cutters, and said third cutter also including a row of teeth spaced from the base row and positioned to cut the area between the areas cut by said two cutters.

2. An earth boring .drill comprising a drill head, three inclined side roller cutters of different axial lengths for cutting an annular area at the side of the drill hole including clearance for the bit head, other roller cutter means adjacent the drill axis for disintegrating a central circular area of the bottom of the hole extending outwardly to said annular area, means attached to the drill head for rotatably supporting the central roller cutter means and the one of the side roller cutters which is of least axial length, and means attached to the drill head for rotatably supporting the other two side cutters.

3. An earth boring drill according to claim 2 in which said central roller cutter means is a single irusto-conical cutter.

4. An earth boring drill according to claim 2 in which the side roller cutters each have an outer; approximately cylindrical cutting surface.

and an inner trusts-conical cutting surface.

5. An earth boring drill comprising three inclined side roller cutters, each having rows of teeth thereon which interflt with rows of teeth of the other side cutters, said cuttersdisintegrating an annular area at the side of the drill including clearance for the bit head, and other rotary cutter means adjacent the drill axis fordisintegrating a central circular area at the bothaving an outer approximately cylindrical cutpositely facing and converge toward eachgother I both laterally and longitudinally or these races.

Iclaim:

1. Anearthboringdrillcomorisimthreerotary 6 1 havins an outermost row of teeth ting surface thereon and also an inner frustoconical cutter surface, and inwardly from one of said cutters and on the same side of the bit axis other cutting means extending to substantially the longitudinal axis of. the drill, said side outters being of larger diameter than said other cutting means.

7. An earth boring drill comprising a drill head, a central roller cutter,'three inclined side roller cutters of different axial lengths. of uniform diameter larger than said center cutter, said side cutters each having rows of teeth positioned thereon in planes inclined .to each other, said center roller cutter being on the same side of the drill axis as one of the side cutters and extending substantially to the spindle means for the cutters attached to the sides of the drill head, and means connecting the inner ends of said spindles together independently or said head.

8. A drill bit comprising three rotary side cutthereon having their cutting edges disposed at cutting surface adjacent said row of teeth, and each of said cutters having one other row of teeth thereon spaced inwardly a diiierent distance than the spacing of the rows of teeth on the other cutters for disintegrating difierent annular areas progressively inwardly from said first mentioned annular area, the cutting edges of ,said other row of teeth of each side cutter being at a different angle to the drill axis from the cutting edges of said outermost rows of teeth to cut in a plane inclined to said annular area at the side of the bore hole, and other rotary cutter means adjacent the drill axis for independent cutting action inwardly of the other cutters and about the axis of the drill bit.

9. A drill bit comprising three rotary side cutters, each having an outermost row of teeth thereon having their cutting edges disposed at an acute angle to the drill axis and tracking each other over an annular area at the side of a, bore hole as the drill is rotated, said annular area inclining downwardly and inwardly, each of said cutters having a. relatively wide groove in its cutting surface adjacent said row of teeth, and each of said cutters having one other row of teeth thereon and positioned in offset relationship to each said other row so as to cut separate annular areas inwardly of the annular area cut by said tracking rows of teeth, and independently rotating cutter means adjacent the drill axis for cutting action inwardly of the other cutters and about the axis of the drill bit.

10. An earth boring drill comprising three cutters mounted to rotate about axes inclining downwardly and inwardly toward the axis of revolution to the drill, the cutters having circumterential rows of teeth thereon, one of the cutters having a wide circumferential groove separating two adjacent rows of teeth, each of the other two cutters having a row of relatively narrow teeth extending into said groove, and an independently rotatable center cutter means.

CLARENCE E. REED. 

